Destruction of the Towers' Steel Remains
The only constituents of the Twin Towers that survived the "collapses" in the form of recognizable pieces of any size were their metal parts, such as pieces of structural steel and aluminum cladding. 1 Virtually all the non-metallic parts of the towers and their contents were converted to microscopic dust particles or small unrecognizable fragments.
Building 7, though also reduced to a short pile of rubble, was not as thoroughly pulverized as the towers. Large sections of the building's perimeter wall could be seen on the rubble pile.
The surviving fragments of steel from the Twin Towers, most of them between 10 and 30 feet in length, and the larger remaining steel sections from Building 7, were essential to any serious investigation of the collapses. These catastrophic failures were at least as deserving of careful study as other rare events that are studied intensively, such as the aviation disasters investigated by the National Transportation Safety Board (NTSB). Normally, great care is taken in preserving the evidence from structural failures and crime scenes.
No such effort was made to preserve the evidence of the unprecedented and unexplained collapses of skyscrapers WTC 1, WTC 2, and Building 7 in lower Manhattan -- easily the three largest and least understood structural failures in World history. Indeed the evidence was destroyed with remarkable speed and efficiency.